When do hardmode ores spawn?

In Terraria after you kill wall of flesh and start a hard mode a new ores such as Cobalt, Mythril etc. should be generated, and it was okay in 1.1 update, but now for some reason these ores are not generated when I kill the wall of flesh.

What is wrong? Or is it my mistake?

Solution 1:

The new ores are generated when you destroy Demon Altars in Corruption or Crimson Altars in the Crimson, not when you kill the Wall of Flesh. Killing the WoF does enable the destruction of Demon Altars, though. Upon defeating the WoF you receive an item called the Pwnhammer, this is what you use to destroy the Demon/Crimson Altars.

Note that they can only be destroyed in any world where the WoF has been beaten, so you can't take a Pwnhammer to a new world and start bashing Demon/Crimson Altars.